Any house painter will tell you that one of the most arduous parts of a job is masking: outlining the edges of window frames and trim with tape to ensure a neat job.

Masking can also be one of the most arduous parts of a Photoshop project, for much the same reason. Isolating a subject from its background can be tedious, especially if there isn’t a lot of contrast between the subject and the background or if the subject has blurry edges or fine details, such as wisps of hair.

Experienced Photoshop artists have employed a variety of masking tricks, and have used such programs as Extensis’ Mask Pro 3 (
,
August 2003
) or Corel’s KnockOut 2 (
,
March 2002
), but now there’s an easier path to tidy masks: Vertus’ Fluid Mask 1.02. A plug-in for Adobe Photoshop, Fluid Mask provides a rich array of tools for isolating portions of an image and then cutting out the portion you want to keep.

Photoshop CS2’s
Extract filter performs the same job, though in my tests, Fluid Mask often created cleaner masks in images containing tricky edges, such as hair or backgrounds whose color is similar to the subject’s. And Fluid Mask lets you preview a mask-in-progress in ways that are faster and more efficient than the Extract filter’s Preview mode.

Fits right in

To use Fluid Mask, open an image and then choose Fluid Mask from Photoshop’s Filter menu. Fluid Mask takes over your screen, replacing Photoshop’s menus and tool palettes with its own (see screenshots). Like Photoshop, Fluid Mask provides single-keystroke shortcuts for its tools and brushes—a nice interface touch.

To isolate part of an image, use Fluid Mask’s tools to specify which colors you want to keep and which ones you want to delete. For straightforward masking jobs—for example, isolating a yellow flower from a solid blue background—you might simply paint across the blue background with the Delete Global brush. When you do, Fluid Mask automatically masks out similar colors that appear throughout the image.

For an image containing a consistent background color, this might be the only step you need to perform. You can then click the Create Cut-Out button and watch while Fluid Mask removes the background, leaving only the flower. Close the Fluid Mask window, and you’re back in Photoshop, with your masked image open and ready to use.

Advanced tools

For more challenging masking jobs—isolating a green frog sitting on a similarly colored leaf—you can employ several other tools that provide more control over the masking process. For example, the Adjust Image Information Layer tool lets you temporarily adjust the contrast and color of an image to make it easier for Fluid Mask to identify the edges that separate areas you want to keep or discard.

Depending on your Mac’s speed and the complexity of your mask, rendering a final image can take 10 seconds or more. Fortunately, you can preview your work by using the Test Render tool: select it and drag a rectangle over part of the image, and Fluid Mask renders just that part of the image.

Fluid Mask’s advanced tools can be daunting, thanks largely to the product’s abysmal documentation, which consists of a couple of poorly written PDFs and a printed reference card that is—I kid you not—printed in light-gray, 5-point type. Some informative QuickTime tutorial movies are included on the Fluid Mask installation CD, but a complex and costly plug-in like this one demands better documentation. Vertus says the reference card has already been reprinted for better legibility and that improved electronic documentation will accompany a future version.

One more quibble: Fluid Mask doesn’t work with 16-bit images. If you prefer to shoot or scan in 16-bit mode to get more headroom for Photoshop adjustments, you’ll have to convert images to 8-bit mode before using Fluid Mask. Vertus says it plans to add 16-bit support to a future version.

Macworld’s buying advice

At $249, which is rather expensive for a plug-in, Fluid Mask 1.02 isn’t for casual Photoshop users or those who need to do masking only occasionally. But if masking and compositing are big parts of your life, Fluid Mask deserves a look. It’s a powerful, if poorly documented, tool.